Phase transitions and ferroelectric behavior in the Pb3(MF6)2 family (M=Ti, V, Cr, Fe, Ga)

Abstract

Theoretical studies of the transition metal-carbonyl systems MCO and M(CO)2, M=Ti, Sc, and V The atomic arrangement in Sr 3 (FeF 6 h determined by von der Miihll [CO R. Acad. Sci. Paris 278, 713 (1974)] differs from a structure of opposite polarity by atomic displacements of 1.3 A or less for F and 0.4 A or less for Sr and Fe. The structure is hence potentially ferroelectric, with an estimated transition temperature Tc to the paraelectric state of about 1160 K: experimentally, Tc = 922 K. The Pb 3 (MF 6h family is isomorphous with Sr 3(FeF 6b and the corresponding T elM) has been measured as 695 (Ti), 635 (V), 550 (Cr), 740 (Fe), and 645 (Ga) K. The respective nonlinear dielectric susceptibilities are 0.010,0.010,0.005,0.045, and O.OIOX 10-12 V-I m. A dielectric anomaly is observed close to Tc in each material at 1 kHz with a maximum permittivity €; of2740 (Ti), 300 (V), 2015 (Cr), 4000 (Fe), and 7800 (Ga). Dielectric losses in each material reach a minimum at the phase transition temperature.

Phase transition at 555 K in nonlinear optic Pb5Cr3F19

“…Differential thermal analyses, made using a Trifux model calorimeter (Thermanalyse SA) with a 190 mg sample and a heating (cooling) rate of 1.3 K min-1, gave a transition temperature of 563.9 K on heating and 535"8 K on cooling, for an average Tc of 549.9 K. The average entropy change (AS) associated with the phase transition is 13(3) J mo1-1 K -1. Both T c and AS are in good agreement with the previous values reported for the composition Pb3Cr2F12 (Abrahams et al, 1984). The atomic arrangement in PbsCr3F19 has not yet been determined, but is anticipated to be similar to that in isostructural PbsW309Flo (Marsh et al, 1985;Arquis-Canouet, Ravez, Chaminade, Hagenmuller, Abrahams & Marsh, 1986).…”

“…Each archetype possesses the attributes of ferroelectricity, undergoing a phase transition to the paraelectric phase at the Curie temperature (Abrahams, Ravez, Simon & Chaminade, 1981;Abrahams, Ravez, Canouet, Grannec & Loiacono, 1984). A phase transition at 550 K with entropy change of 17(2)J mol-1 K-1 has been reported in Pb3(CrF6) 2 on the basis of a calorimetric and dielectric permittivity study (Abrahams et al, 1984). The present paper reports the thermal dependence of the unit-cell dimensions and uniaxial indicatrix in this crystal between 295 and 610 K. Accurate density measurement shows that the stoichiometric composition is given by the formula PbsCr3Fx9, not Pb3(CrF6) 2.…”

“…The correct composition is hence PbsCr3F19, in agreement with that recently determined for PbsW309Flo (Marsh, Abrahams & Ravez, 1985). The second-order nonlinear dielectric susceptibility of PbsCr3F19 may thus be taken as 0.005(1) x 10-1 V-1 m (Abrahams et al, 1984).…”

Structurally based prediction of ferroelectricity in inorganic materials with point group 6mm

“…Application of the structural basis for ferroelectricity (Abrahams & Keve, 1971) led to the successful prediction of this property in SrA1F 5 (Abrahams, Ravez, Simon & Chaminade, 1981) and in Pb3(MF6) 2 with M = Ti, V, Cr, Fe and Ga (Abrahams, Ravez, Canouet, Grannec & Loiacono, 1984) on the basis of atomic coordinates previously determined respectively in SrAIF 5 and in Sr3(FeF6) 2 for unrelated reasons.…”

Search for Pnma materials with high-temperature structural phase transitions

“…In the last decade a method for searching for new ferroelectrics based on structural data has been proposed and applied with great success (Abrahams et al, 1984;Abrahams, 1988Abrahams, , 1989Abrahams, , 1990. Polar structures having atomic displacements smaller than 1 A Ê with respect to a hypothetical non-polar con®guration were considered as materials with a high probability of having a phase transition into this con®guration at a higher temperature.…”